1. Field
The disclosure relates to circuit design, and in particular, to an efficient mixer-transconductance interface.
2. Background
Communications circuitry may employ one or more mixer circuits to translate a signal spectrum from one frequency to another frequency. For example, in a transmitter, a mixer may be used in an upconverter to convert a baseband signal to a radio-frequency (RF) signal. In a receiver, a mixer may be used in a downconverter to convert a received RF signal to an intermediate frequency (IF) or baseband for processing. Certain mixer circuits may utilize a current-mode architecture wherein a first input voltage is mixed with a signal current, e.g., a bias current of the mixer, to generate an output signal. The signal current may be generated by a transconductance (Gm) block, which in turn generates the signal current from a second input voltage. In some implementations, both the mixer and the Gm block may be provided with multiple gain settings to tune the overall gain of the mixer-transconductance block.
In multi-band or multi-mode transceivers, multiple instances of the mixer and/or Gm block may be provided to accommodate operation in each separate signal path or mode. This may require certain portions of the mixer-transconductance block to be replicated to support the multiple modes of operation. Furthermore, the mixer may be required to process complex signals, i.e., signals having both an in-phase (I) and quadrature (Q) component. The amount of added circuitry required to support multi-mode and complex operation may unacceptably increase the integrated circuit (IC) die area, as well as increase the number of signal leads in the interface between the mixer and the Gm block.
It would be desirable to provide an efficient architecture for a mixer and a Gm block that provides multiple gain settings for the mixer-transconductance block, and which further efficiently accommodates mixing of complex signals for multi-mode operation.